> I never found it necessary to "adjust" the bias. I use 50 watt zeners
> to obtain the correct ZSAC, and it stays there. I use 8 volt units for
> an 8877 with 2500-3000 volts Ep and a 12 volt unit for 4kv Ep. If I
> want to cut ambient heat when on CW, I just switch to another 50 watt
> zener of the proper value to lower the ZSAC to an appropriate value.
>
> //Good point, Phil. I do exactly the same thing. I've used strings of
> rectifiers, forward biased, to provide the positive cathode bias required
> for tubes when "experimenting," but I don't leave them there, I replace
> them with a fixed value DO-5 50W zener, or whatever's appropriate. The
> forward voltage curve (Vf/If) of rectifiers isn't very stable, has a
> fairly high temperature coefficient, etc. A standard 3A rectifier like a
> 1N54xx series device has Vf < 0.1 at 10mA and close to 1.0 at 3A. Not my
> idea of a "regulator."
>
> -WB2WIK/6
>
>
> IMO, "strings" of components, marginal tank components, non-RF rated
> capacitors, and 3-4 tubes are only found in amateur equipment.
>
> To each his own; I am just not a "Rube Goldberg" type when it comes
> to amp building!
>
> (((73)))
> Phil, K5PC
>
>
|